1. Field of the Invention
The present invention relates to a toothed belt, and more particularly to a skew-toothed belt for power transmission and to a method for manufacturing the skew-toothed belt.
2. Description of the Related Art
FIGS. 3A and 3B are a perspective view showing the appearance of a conventional toothed belt, and a bottom view showing the arrangement of the weft f as viewed from the teeth side. The toothed belt includes core yarns, or tension members 11, a tooth portion 12, and a back portion 13. The tooth portion 12 and the back portion 13 are located on opposite sides of an array of the tension members 11 and are formed of tooth rubber and back rubber, respectively. The side of the toothed belt on which teeth are formed is called the tooth side. The tooth side is covered with a tooth cloth 14. The warp and the weft f, which are multifilament yarns of polyamide or a like material, are woven into the tooth cloth 14. The tooth cloth 14 is usually arranged such that the warp extends in the width direction of the belt and such that the weft f extends in the longitudinal direction of the belt.
FIG. 4 shows a portion of a process for manufacturing such a toothed belt. As shown in FIG. 4, in a cutting step for cutting out the tooth cloth 14, an elongated tooth cloth material 14a impregnated with rubber dough is cut in the width direction thereof, i.e., along the weft arrangement, thereby obtaining a tooth cloth sheet 14b. The opposite end portions of the tooth cloth sheet 14b extending along the warp are bonded together to form a cylindrical tooth cloth 14c. The cylindrical tooth cloth 14c is fitted onto a cylindrical die 20', on the circumference of which are formed axially-extending tooth-profiled grooves 21'. Then, the adhesive-applied tension members (not shown but see the one 11 shown in FIG. 3A) are wound onto the cylindrical tooth cloth 14c. Further, an unvulcanized rubber compound sheet, which will become tooth rubber and back rubber, is wound onto the wound tension members. The resultant assembly is subjected to forming and vulcanization in a pressure chamber. Subsequently, the resultant cylindrical body is cut into annular toothed belts, each having a predetermined width.
In the thus-obtained annular toothed belt, as shown in FIG. 3B, the weft f extends in the longitudinal direction of the belt. Thus, the warp interlaced with the weft f extends in the width direction of the belt. Accordingly, the stretchability of the weft f itself helps the tooth cloth 14 follow the tooth profile intimately.
Thus, in the case of a toothed belt whose tooth trace direction is perpendicular to the longitudinal direction of the belt, i.e., whose teeth are not skewed, the tooth cloth 14 follows the tooth profile intimately, so that the teeth are profiled to a high degree of accuracy, thereby establishing good engagement with a pulley.
However, in FIG. 6, in order to manufacture a toothed belt whose tooth trace direction is oblique to the longitudinal direction thereof, i.e., a skew-toothed belt, the method for cutting the tooth cloth 14b as shown in FIG. 4 is combined with a cylindrical die 20 on the circumference of which are formed tooth-profiled grooves 21 extending obliquely to the axis thereof. In such a case, the weft f extends in the longitudinal direction of the belt, but obliquely to the tooth trace direction, as shown in FIG. 5B. As a result, the stretchability of the weft f becomes insufficient during forming and vulcanization in a pressure chamber, and thus the tooth cloth follows the tooth profile poorly.
Therefore, the skewed teeth fail to be profiled as desired, resulting in a potential failure to smoothly engage a pulley and thus raising various problems in terms of ability to reduce the size of a skew-toothed belt, power transmission rate, durability, applications, and reliability.